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If you want to jump in a car and smoke some weed on Monday when recreational use of marijuana becomes legal in California, think again.

A new state law makes smoking marijuana while driving or riding as a passenger illegal — a move to combat a type of intoxicated driving officials fear may become more common and more dangerous.

The Christmas Eve death of CHP officer Andrew Camilleri is being blamed on a speeding driver who may have been drunk and stoned when he got behind the wheel and headed south on Interstate 880 and smashed into the highway patrol vehicle parked on the shoulder.

CHP Assistant Chief Ernest Sanchez said Monday the driver was coming home from a party, and “obviously had too much to drink and too much to smoke.”

Alcohol-impaired driving is still the most serious problem on California roads. However, since 2006, the percentage of drivers in fatal collisions who have other impairing substances in their system — including THC, the active ingredient in marijuana — has soared to 38.7 percent.

And the push has led to a new message on electronic freeway signs that go beyond drunken driving warnings: “DUI Doesn’t Just Mean Booze” or “Drive high, get a DUI.”

But there’s a challenge in enforcing DUI laws when it comes to marijuana: Unlike with booze and the well-known 0.08 blood alcohol concentration limit, the state has not defined in law a measurable amount of THC that is illegal. Police can conduct a field sobriety test, and — under the new law — ticket anyone they see smoking weed in a moving vehicle. State leaders continue to debate whether those regulations will be sufficient.

Still, it’s clear to many that the problem is on the rise.

Said State Sen. Jerry Hill, D-San Mateo, one of the sponsors of the new law: “Buzzed driving is impaired driving and buzzed motorists don’t belong on the road.”

While some drivers scoff at those reports — “marijuana is as American as apple pie, and healthier,” said motorist Jon Thomas — others are worried.

Thomas Bougher says he was nearly hit by a red-light runner while walking his dogs along Santa Teresa Boulevard in San Jose and witnessed a passenger in the car smoking a joint.

“It was close to a scene out of a Cheech and Chong movie,” he said. “Traffic and drivers are crazy enough as it is.”

Nathan Grieg of Belmont says he often gets a whiff a marijuana as cars pass him with their windows open.

“Hardly a day goes by, especially in summer, when I do not smell the pungent odor of marijuana wafting out of an open car window,” he said.

And retired San Jose cop Joe Wicker said he’s seen the ravages of traffic accidents that involved alcohol and drugs.

“The legalization of marijuana will just cause more problems on our roads,” he said.

Safety officials gathered Wednesday in Sacramento — just blocks away for a bill ringing memorial for the fallen CHP officer — to spread the word that you need to put the weed away when traveling.

The CHP has given officers across the state including city cops 72 hours of updated training amid worries that new users may be unaware of the risks they pose when behind the wheel.

“That’s the message we are trying to get out now,” spokesperson Fran Clader said. “Stay away from behind the wheel. New users may not be aware of the effect there will be.”

In Washington, fatal crashes involving marijuana doubled after the state legalized it in 2012, according to AAA. The percentage of drivers involved in fatal crashes who recently used marijuana more than doubled from eight to 17 percent between 2013 and 2014. One in 6 drivers involved in fatal crashes in 2014 had recently used marijuana, the automobile agency reported.

“You should be holding the steering wheel — not a joint or an edible,” said Santa Clara County District Attorney Jeff Rosen when the tougher restrictions were announced. “There is nothing recreational, medicinal or legal about hurting someone in a car accident when you’re high. Please don’t do it.”

Look for Gary Richards at Facebook.com/mr.roadshow or contact him at mrroadshow@bayareanewsgroup.com.

The Cost of Smoking Pot and Driving

Penalties for smoking marijuana in a car begin at $70 but could be as much as $10,000 or similar to the cost of a drunk driving ticket if injuries or deaths are involved and insurance rates can skyrocket.

California has earmarked $3 million for training police to better understand when drivers may be under the influence of marijuana. That is the highest level in the nation.

Gary Richards has covered traffic and transportation in the Bay Area as Mr. Roadshow since 1992. Prior to that he was an assistant sports editor at the paper from 1984-1987. He started his journalism career as a sports editor in Iowa in 1975.